Mortar was used as a matrix material in an immobilization process of radioactive waste material, 137CsCl solution, where the final product had a water-to-cement ratio of 0.36. Solidified orthocylinder shaped samples, H=4.5 cm, with the exposed surface area completely open to contact leachant medium, were used in prospecting physico-chemical and mechanical characteristics of mortar-radwaste mixture forms. After curing period of 28 days in an atmosphere of defined parameters, samples were introduced to leaching in the specific leachant media. Leachants were chosen up to their aggressive influence on matrix material deterioration and decomposition: distilled water, chloride and sulphate solutions. Experiments were performed for 730 days and the 137Cs cumulative leached fraction for each leachant was calculated. Leach-rate steady-state values were obtained after approximately 290 days. The same trend in obtaining saturation value was noticed in an investigations of pH value and Ca2+ concentration in the three groups of leachants, due to a Ca2+ depletion from the matrix structure. Mortar-radwaste mixture samples were withdrawn from the leaching experiments and investigated on their mechanical strength. Mechanical strength characteristics adopted a decreasing trend for the samples treated in leachants longer than 100 days, which continued in the two years period of experimental duration.